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Romero R.,Institute Recursos Naturales y Agrobiologia IRNASE CSIC | Muriel J.L.,IFAPA Las Torres Tomejil | Garcia I.,IFAPA Las Torres Tomejil | Munoz de la Pena D.,University of Seville
Agricultural Water Management | Year: 2012

Availability of fresh water is one of the elementary conditions for life on Earth, however, water is a limited resource, which is now under an unprecedented pressure by global population growth, climate change and demand from several economic sectors such as tourism, industry, and agriculture. In particular, irrigated agriculture is one of the major water-consuming sectors. The aforementioned issues justify the need for a sustainable and rational use of water in irrigated crops, which motivates the implementation of new precise automatic irrigation technologies based on control theory. In this paper, we introduce the main concepts of control theory, how can it be applied to irrigation and a literature review of automatic irrigation control systems over the last decade. In addition, we present our latest developments in this field. In particular, we present some promising preliminary experimental results of four different control strategies applied to fruit trees in southern Spain to show the potential of the application of control techniques to irrigation. © 2012 Elsevier B.V.


Sperry J.S.,University of Utah | Christman M.A.,Institute for Ecohydrology Research | Torres-Ruiz J.M.,Institute Recursos Naturales y Agrobiologia IRNASE CSIC | Taneda H.,University of Tokyo | Smith D.D.,University of Utah
Plant, Cell and Environment | Year: 2012

Vulnerability curves using the 'Cavitron' centrifuge rotor yield anomalous results when vessels extend from the end of the stem segment to the centre ('open-to-centre' vessels). Curves showing a decline in conductivity at modest xylem pressures ('r' shaped) have been attributed to this artefact. We determined whether the original centrifugal method with its different rotor is influenced by open-to-centre vessels. Increasing the proportion of open-to-centre vessels by shortening stems had no substantial effect in four species. Nor was there more embolism at the segment end versus centre as seen in the Cavitron. The dehydration method yielded an 'r' shaped curve in Quercus gambelii that was similar to centrifuged stems with 86% open-to-centre vessels. Both 'r' and 's' (sigmoidal) curves from Cercocarpus intricatus were consistent with each other, differing only in whether native embolism had been removed. An 'r' shaped centrifuge curve in Olea europaea was indistinguishable from the loss of conductivity caused by forcing air directly across vessel end-walls. We conclude that centrifuge curves on long-vesselled material are not always prone to the open vessel artefact when the original rotor design is used, and 'r' shaped curves are not necessarily artefacts. Nevertheless, confirming curves with native embolism and dehydration data is recommended. An 'r' shaped vulnerability curve shows an initially steep decline in the hydraulic conductivity of xylem, indicative of a population of xylem vessels that are extremely vulnerable to cavitation. Is this type of curve an artifact of the widely used centrifugal method, and is the 'r' shape related to the number of 'open' vessels that are exposed at the ends of the sample? Not according to our results because: a) curves were relatively insensitive to the number of open vessels, b) there was no anomalous embolism at segment ends, and c) 'r' shaped centrifuge curves were consistent with 'r' shaped curves from branch dehydration and single-ended air injection. Nevertheless, 'r' shaped curves invite deserved skepticism and should be checked against native conductivity measurements or dehydration curves. © 2011 Blackwell Publishing Ltd.


Cuevas M.V.,Institute Recursos Naturales y Agrobiologia IRNASE CSIC | Torres-Ruiz J.M.,Institute Recursos Naturales y Agrobiologia IRNASE CSIC | Alvarez R.,Verdtech Nuevo Campo S.A. | Jimenez M.D.,Verdtech Nuevo Campo S.A. | And 2 more authors.
Agricultural Water Management | Year: 2010

Plant age and size, seasonal growth patters and crop load, among other factors, have been reported to decrease the usefulness of trunk diameter variation (TDV) derived indices as water stress indicators in olive trees. Our hypothesis, however, is that indices derived from TDV records in old, big olive trees are sensitive enough to detect levels of water stress in trees of orchards under deficit irrigation that, although severe, are below the threshold for fruit shrivelling. This is of importance for the production of good quality oils, since fruit shrivelling may affect oil quality. The aim of this work was to assess different TDV-derived indices as water stress indicators in 40-year-old 'Manzanilla' olive trees with heavy crop load. We derived the maximum daily shrinkage (MDS), daily growth (DG) and daily recovery (DR) from TDV records taken during the 2008 dry season both in well-irrigated FAO trees and in deficit-irrigated RI trees. Measurements of volumetric soil water content (θv), leaf water potential (Ψl), stomatal conductance (gs), net CO2 assimilation rate (A), water and oil accumulation in the fruits and yield parameters were made for both treatments. The trunks did not grow during the experimental season, either in the FAO or RI trees, likely because of the heavy crop load. Therefore, DG was useless as water stress indicator. For MDS and DR, which were responsive to the increase of the trees' water stress, we calculated the variability, quantified by the coefficient of variation (CV), the signal intensity (SI) and the sensitivity (SI/CV) values. In addition, we derived reference equations for irrigation scheduling from the relationships between MDS values in the FAO trees and main meteorological variables. Values both of SI-MDS and SI-DR were steady until September 9, despite of increasing differences in θv between treatments from early in the dry season. The Ψl vs θv values showed an outstanding capacity of the RI trees to take up water from the drying soil, and the Ψl vs gs values showed a near-isohydric behaviour of those deficit-irrigated trees. These results explain, at least in part, the lack of response of MDS and DR on that period. Both SI-MDS and SI-DR peaked for the first time on September 9, 16 days before the appearance of fruit shrivelling. Our results suggest that using TDV-derived indices as water stress indicators for irrigation scheduling in old olive orchards with medium to low plant densities, i.e. with large root zones, may be useless in case the irrigation strategy is aimed at keeping the soil close to field capacity. Nevertheless, the MDS and DR indices may be useful indicators for the avoidance of fruit shrivelling in deficit irrigated olive orchards for the production of good quality oil. Reliable reference equations for scheduling irrigation with the signal intensity approach were obtained from the regression of MDS values vs the daily maximum values of both the air temperature and the vapour pressure deficit of the air. © 2010 Elsevier B.V. All rights reserved.


Fernandez J.E.,Institute Recursos Naturales y Agrobiologia IRNASE CSIC | Torres-Ruiz J.M.,Institute Recursos Naturales y Agrobiologia IRNASE CSIC | Diaz-Espejo A.,Institute Recursos Naturales y Agrobiologia IRNASE CSIC | Montero A.,Institute Recursos Naturales y Agrobiologia IRNASE CSIC | And 4 more authors.
Agricultural Water Management | Year: 2011

Olive is one of the fruit tree species for which measurements of the trunk diameter variation (TDV) has shown a lower potential both for monitoring water stress and for scheduling irrigation. This is particularly true in the case of old, big olive trees with heavy fruit load. Fernández et al. (2011, J. Environ. Exp. Bot. 72, 330-338) observed that the daily difference for maximum trunk diameter between deficit irrigated 'Manzanilla' olive trees and control trees growing under non-limiting soil water conditions, termed DMXTD, is more sensitive and reliable for detecting the water stress of the trees than other widely used TDV-derived indices. However, they considered their results as preliminary because of the lack of replications. The aim of this work was to evaluate the usefulness of the DMXTD index for detecting plant water stress in an orchard with 12-year-old 'Arbequina' olive trees with heavy fruit load. The performance of DMXTD for detecting water stress of the trees was compared to that of the signal intensity for the maximum daily shrinkage (SI-MDS) derived from the same TDV records. Results showed that SI-MDS was not useful for indicating the water stress of the trees. On the other hand, the dynamics of DMXTD mimicked those of the soil and plant water status. Four instrumented trees per treatment (replicates) were enough to reduce the uncertainty of the TDV measurements to a reasonable level. Our results show that DMXTD is a useful index to detect the onset, and severity, of water stress in mature 'Arbequina' olive trees with heavy fruit load. They also suggest a potential of DMXTD for scheduling low frequency deficit irrigation strategies. © 2011 Elsevier B.V.

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